This invention relates to a method of and an apparatus for feeding and discharging air to and from a pneumatic jig, which is used to separate a pulverulent body in accordance with the differences in the specific gravity of particles thereof.
First, a pneumatic jig will be described with reference to FIGS. 1 and 2. Partitions 2 provided in a casing 1 defines therein a plurality of water tanks 3, each of which is provided with an air chamber 4 therein. A reticulate member 5 is provided at upper portions of the water tanks 3, and a feed port 6 for a pulverulent body at an upper portion of one end of the casing 1, discharge ports 7, 8 for lighter and heavier pulverulent bodies, respectively, being provided in a vertically adjoined state at an upper portion of the other end thereof. Each of the air chambers 4 is provided therein with an air pipe 9 extended therethrough from the outside of the casing 1, while each of the water tanks 3 is provided at a lower portion thereof with a water pipe 10 extended therethrough from the outside of the casing 1.
Water is stored in each of the water tanks 3. A pulverulent body is fed from the feed port 6 onto the reticulate member 5. The pressure air is fed and discharged periodically to and from the air chambers 4 through the air pipes 9. Owing to the periodical feeding and discharging of the pressure air, the water-level in the water tanks 3 is displaced up and down repeatedly. Such vertical displacement of the water-level cause the pulverulent body, which has been fed from the feed port 6 onto the reticulate member 5, to be moved vertically as it is agitated. Consequently, the pulverulent body is stratified or separated into an upper layer consisting of particles thereof having a lower specific gravity, and a lower layer consisting of particles thereof having a higher specific gravity. The stratified pulverulent body is moved from the feed port 6 toward a downstream end of the casing 1. Such particles of the pulverulent body that have a lower specific gravity are recovered from the upper discharge port 7 with the overflowing water, while such particles thereof that have a higher specific gravity are moved on the reticulate member 5 to be recovered from the discharge port 8.
While the above-described operation is repeated continuously, the pulverulent body, which is fed from the feed port 6, is separated into particles having a lower specific gravity and particles having a higher specific gravity. In order to prevent the quantity of water in the water tanks 3 from decreasing below a predetermined level, the water is supplied thereto constantly through the water pipes 10.
In order to feed and discharge pressure air to and from the air chambers 4 in the above pneumatic jig through the air pipes 9, an air feeding and discharging apparatus shown in FIGS. 3 and 4 has heretofore been used.
Referring to FIGS. 3 and 4, an air feed port 12 and an air discharge port 13, which are communicated with a pressure air feeding means (not shown), are provided in those portions of a circumferential wall of an outer cylindrical casing 11 which are opposed to each other. A communication port 14, which is communicated with the air pipes 9 shown in FIGS. 1 and 2, is provided at a lower portion of the outer casing 11. Inside the outer casing 11, an inner cylindrical casing 15, which is rotated at a constant speed by a drive means (not shown), is provided. The outer surface of the inner casing 15 and the inner surface of the outer casing 11 are air-tightly formed. The inner casing 15 is opened at both ends thereof, so that the interior thereof and the communication port 14 are communicated with each other. The inner casing 15 is provided with a communication port 16 in a circumferential wall thereof. Reference numerals 17, 18 denote slide gates for use in regulating the areas of the air feed and discharge ports 12, 13.
When the inner casing 15 is rotated to allow the communication port 16 to be opposed to the air feed port 12, the pressure air flows into the interior of the inner casing 15 through the air feed port 12 and communication port 16. The pressure air then flows from the interior of the inner casing 15 to the communication port 14 through both end portions of the former. The pressure air then flows from the communication port 14 into the air chambers 4 through the air pipes 9.
When the inner casing 15 further continues to be rotated, the air feed port 12 is closed with the outer surface thereof, so that the pressure air stops flowing into the inner casing 15. When the inner casing 15 further continues to be rotated, the communication port 16 is opposed to the discharge port 13. When the communication port 16 is opposed to the discharge port 13, the air in the air chambers 4 flows from both end portions of the inner casing 15 thereinto through the air pipes 9 and communication port 14. The resulting air is discharged to the atmosphere through the communication port 16 and discharge port 13.
The air is thus fed and discharged alternately to and from the air chambers 4. The pressure in the air chambers 4 is increased and decreased in accordance with upwardly extending mountain-shaped sine curves shown in FIG. 5a, while the water in the water tanks 3 is vibrated in accordance with a sine curve shown in FIG. 5b, which waves in a staggered manner with respect to the sine curves shown in FIG. 5a. However, when the water is vibrated in such a manner, the pulverulent body fed onto the reticulate member 5 receives either the upward or downward force of water at all times in a substantially equal manner, so that the time necessary for the pulverulent body to fall freely and thereby promote the separation thereof is too short. This causes a decrease in the separation efficiency of the pulverulent body.